I many times see the Pn wave in regionals
from California but not from Baja California.

I have tables that address the distances related to
this phase.

It seems to me the Pn is an order in magnitude less
than the Pg wave.

Not sure the magnitudes are different or these
phases are additive.

Like Pn adds to Pg and thats why Pg seems
greater in intensity ?

Also, S waves do not travel through liquids.
Are there magma chambers that may be intefereing
with arrivals of S waves from any givin direction ?

Are there maps of magma chambers in the southwestern
USA ?

The closer you or the earthquake is to a magma chamber
may effect who sees what.

geoff
----- Original Message ----- 
From: "Dave Wolny" 
To: 
Sent: Thursday, September 03, 2009 6:04 AM
Subject: RE: ARRIVAL TIMES: Quiet Before The Storm


Between distances of around 100-800 km you may see a refracted P wave.  I believe it is referenced as a Pn wave.  The refracted P 
wave will arrive before the true P wave.  If you are using Larry's Winquake, that phase is available in the tables.  Be sure to turn 
on Sn as well.

I'm doing this from memory, so don't hold it against me if that isn't exactly correct.

Dave

>>> "Steve Hammond"  09/02/09 11:06 PM >>>
I also noticed an anomaly in local events within 20-25km south of my old San
Jose location when I lived in south San Jose. My house was located between
the San Andreas and Calaveras faults and I had data from both faults that
had something going on just before the P wave arrived. I showed John Lahr
the data and asked if there was such a thing as  a  pre-P wave and he told
me there was not. I finally figured that it was a just a flaw in the sensor.


Regards, Steve Hammond

From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of Barry Lotz
Sent: Wednesday, September 02, 2009 6:54 PM
To: psn-l@..............
Subject: Re: ARRIVAL TIMES: Quiet Before The Storm




Geoffrey
I've also noticed this for quite some time. I thought it was my sensors.
Maybe not.
Regards
Barry


--- On Wed, 9/2/09, Geoffrey  wrote:


From: Geoffrey 
Subject: ARRIVAL TIMES: Quiet Before The Storm
To: "PSN-LIST" 
Date: Wednesday, September 2, 2009, 5:50 PM

I have noticed in some Earthquakes you seem to notice
a short increase in quietness just before the impulse arrives.

Is this a real phenomena or simply a coincidence ?

Does this mean the real arrival time is
the beginning of the noticeable quiet ?

WHY THE QUIET ??
What physics would possibly muffle the noise ?

arrival of Possibly eP instead of simply P ?

Also,

What is the preferred format for a PSN files data ?
FLOAT or INTEGER
16 bit or 32 ?

My data is all 8 bit So should I expand it to
meet the new format ?

Comments ?

geoff
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